The Histopathology Shared Resource provides AECC investigators with a full range of histotechnology and histopathology services with a major focus on mouse models of human cancers. The facility also supports the veterinary services of the AECC Animal Barrier Shared Resource where AECC investigators' mice are housed. The facility provides necropsy and histopathology services for phenotypic analysis along with a full range of histological services including tissue preparation, paraffin and frozen embedding, standard and specialized stains and immunohistochemical analyses to meet the needs of AECC investigators. Several new techniques have been added since the last CCSG review. These include: (1) Staining with the new 'polymer' technology which negates the need for avidin/biotin based staining giving less background staining and reducing protocol length. (2) Immunohistochemical characterization of multiple proliferation markers in the mouse (BrdU, Ki67, PCNA, and pRb) that allows the investigator to choose different proliferative windows, with or without special experimental manipulation prior to sacrifice. (3) Immunohistochemical detection of LacZ protein, which is more sensitive and specific than X-gal staining, and allows integration of this marker into standard paraffin-section based histology. (4) Immunoalkaline phosphatase detection with a new fuchsin substrate that allows xylene-based mounting and higher resolution than aqueous mounting. (5) Double antibody detection combining immunoperoxidase with DAB-nickel detection, and immunoalkaline phosphates with new fuchsin detection. (6) Immunofluorescence protocols for conventional paraffin sections, utilizing fluors with spectra that do not overlap with tissue autofluorescence, and blocking agents that quench autofluorescence. This allows immunohistochemical and conventional light microscopic analyses to be carried out on consecutive sections of routinely processed tissue specimens. A Chemicon Tissue Arrayer was recently acquired for the production of custom tissue arrays. The facility provides consultative support and training to members, their trainees, and their staff. The facility faculty leader, Dr. Rani Sellers, and director, Dr. Radma Mahmood are highly experienced in histotechnology and histopathology with a broad capability in the characterization of mouse models and developmental defects associated with the genetic changes that are induced in animals.